Appending a list in a class from a callback function

[snizbatch]

I've simplified my question a bit here to see if anyone can help me with this. When I run the following IP Scan, the results print fine from within the callback function. The whole list will even appear if I do a print() of self.mac_list from within the callback function. However, when the routine terminates and go() returns self.mac_list it is always empty. Anyone know what I am missing here?

Thanks,
Jim

import nmap

class IP_Roam():
    def __init__(self, root_ip="", display_on=False):
        self.mac_list = []

    def callback_result(host, scan_result):
        print(scan_result)
        self.mac_list.append(scan_result)

    def go():
        nma = nmap.PortScannerAsync()
        nma.scan(hosts='192.168.1.0/30', arguments='-sP', callback=callback_result)

        while nma.still_scanning():
            print("Waiting >>>")
            nma.wait(2)   # you can do whatever you want but I choose to wait after the end of the scan
        return self.mac_list


if __name__ == "__main__":
    ps = IP_Roam()
    results = ps.go()
    print(results)